THE VALENCY RULE AND THE HOFMEISTER SERIES 69 



tions was not retained, the pH rising higher inside than outside in 

 the case of solutions of gelatin-acid salts. The observations 

 lasted usually for 1 day but the level of liquid in each manometer 

 was recorded at first every 20 or 30 minutes and the values 

 recorded the next day were used to plot the curves in Fig. 14. 

 The osmotic equilibrium was usually established in about 6 

 hours. The experiments were carried on in a thermostat at a 

 temperature of 24C. 



Figure 14 gives the curves of the osmotic pressure for solutions 

 of originally 1 per cent isoelectric gelatin with four different 

 acids, HC1, H 2 S04, oxalic, and phosphoric acids. 1 The abscissae 

 are the pH of the gelatin solutions after osmotic equilibrium was 

 established, i.e., at the end of the experiment. The pH was 

 always determined potentiometrically. The reader will notice 

 that the four curves have a number of characteristic features in 

 common. The osmotic pressure is, in all cases, a minimum at 

 the isoelectric point, namely, at pH = 4.7; it rises with increasing 

 hydrogen ion concentration (or diminishing pH) , and the curves 

 all reach a maximum at about pH = 3.4. When the hydrogen 

 ion concentration rises still further (or with a further drop in pH) 

 the curves for the osmotic pressure of the solutions of the four 

 gelatin salts diminish almost as steeply as they rose on the other 

 side of the maximum. It may be noticed in passing, that Pauli 2 

 and Manabe and Matula 3 speak of a maximum in the viscosity 

 curves of albumin at a pH of about 2.1. It will be observed that 

 the maximum for osmotic pressure lies at a much higher pH, 

 namely at about pH 3.4, and that at pH 2.1 the curves are at a low 

 level again, not much above that of the isoelectric point. This 

 form of the curves of osmotic pressure when plotted as a func- 

 tion of pH of the protein solutions is very characteristic and 

 invariable. 



The main point, however, which interests us in this connection 

 is the proof of the valency rule. The titration curves show that 

 in the case of gelatin phosphate as well as of gelatin chloride the 

 anion is monovalent, H 2 P04 and Cl. The valency rule demands 



1 LOEB, J., J. Gen. PhysioL, vol. 3, p. 691, 1920-21. 



2 PAULI, W., " Kolloidchemie der Eiweisskorper," Dresden and Leipsic, 

 1920. 



3 MANABE, K., and MATULA, J., Biochem. Z., vol. 52, p. 369, 1913. 



